Meaning of Drop in LH surge


I have a basic question on LH surge. My LH surge doesn’t seem like it lasts more than 8 Hours on an average. That is if I have a positive ppl at 9 am by 6 pm opk would indicate close positive aka test line is little lighter to control line.

Does have similar experience with LH surge.? What does this actually mean, is my fertile window (ovulation is completed and hence starts dropping) is closed once the LH surge starts dropping?